The present invention relates in general to a casting apparatus for electrophoretic gel trays, and more particularly, to such an apparatus adapted for casting a separation medium such as agarose and polyacrylamide gel solution in an open-ended gel tray for horizontal gel electrophoresis. Application of such electrophoretic gels includes the separation and analysis of DNA, RNA, and other molecules of interest.
Electrophoresis is an analytical method widely used in research and clinical analytical processes. A variety of electrophoretic techniques are employed, including thin-layer, column, and upright slab gel electrophoresis, however, the present invention is a method for producing a gel for horizontal electrophoresis. While other substances and molecules may be subjected to horizontal electrophoresis, this technique is most widely used to separate and analyze nucleic acids such as DNA or RNA molecules. The source of these molecules may be tissue or cells from living or dead organisms, or from cultured cells. Molecules of interest also may be synthetically generated by PCR, RT-PCR, oligonucleotide synthesis, or other laboratory methods.
The general principle of electrophoresis is the movement of molecules in a mixture through a medium capable of retarding the movement of the molecules as a function of molecular weight, charge, size or conformation. The driving force is most frequently an applied electrical field through the medium. The typical embodiment of this medium is an agarose gel of a predetermined thickness submerged in a buffer capable of transferring an electrical charge. The ends of the gel are generally open to the buffer to allow the electrical current to enter one end of the gel, pass through the gel, and exit the other end through the buffer. In this manner, molecules are compelled to move through the gel and may be separated from each other.
In order to cast a gel, the ends of a gel tray that are open during the electrophoresis process must be temporarily blocked during the casting process so as to form a mold. A second toothed-mold called a comb is placed within the gel tray mold so that tooth-shaped wells will be formed in the gel. A solution of agarose, acrylamide, or other suitable media is poured into the gel tray mold and allowed to cool and polymerize. When the gel has polymerized, the temporary blocks are removed from the ends of the tray, and the comb is lifted from the gel. The gel and its supporting gel tray are transferred to an electrophoresis box and submerged in electrophoretic buffer. Samples of mixtures to be analyzed are placed in the wells and subjected to electrophoresis.
Despite the variety of commercially available gel casting apparatuses, the most widely used method for blocking the open ends of the tray is still the manual application of tape. Persistence of the use of tape is due to lack of a versatile apparatus that can accommodate a wide variety of gel tray and/or comb sizes and shapes, as well as failure of currently available products to hold a reliably liquid-tight seal. While taping the ends of the trays is generally satisfactory and will usually work with most gel trays, there are some gel tray designs with base pieces extending beyond the side walls, thus making it difficult to reliably seal the ends. However, this is not a problem limited to those certain gel tray designs. Tape adhesion can fail with a gel tray of any design, since the heat of liquid agarose can cause loss of adhesion and leakage when the liquid agarose is poured into the taped tray. Heat-resistant tape of a suitable adhesive quality is fairly costly, and over time, can amount to a considerable expense. While some commercially available casting systems seal adequately, they require the use of a specific gel electrophoresis box and gel tray system and cannot accommodate trays and/or combs from other manufacturers. Furthermore, high temperatures of liquid agarose can cause temporary or permanent warping of the gel tray and/or gasket pieces in some systems and compromise the integrity of the seal. Some systems also require the use of locking bolts or other loose parts that may break or be lost easily, further decreasing the utility of such systems. Currently, there is no quick and easy way to reliably block the ends of a wide variety of gel tray styles and sizes using a single apparatus.
It is broadly an object of the present invention to provide a casting apparatus for electrophoretic gel trays specifically adapted for nucleic acid electrophoresis systems which provides a liquid-tight seal for the purpose of casting an electrophoretic gel of a predetermined thickness. It is also an object of the present invention to provide a rapid means of preparing an open-ended gel tray for the purpose of casting an electrophoretic gel, the function of which is unaffected by the heat of a typical gel solution.
The casting apparatus described in this application rapidly and reliably creates a liquid-tight seal at each end of a gel tray. The casting apparatus can accommodate gel trays of varying sizes, including those originally designed to work only as components within specially designed systems. The design of the casting apparatus does not interfere with placement of combs within gel trays. Unlike tape, the structure of the present invention is durable and reusable. The high heat of a typical gel solution does not affect the performance of the present invention. The versatility and reusability make the present invention more useful and economical than any other system in the prior art, including the use of tape. In addition, it is compact enough to be placed in a refrigerator to enhance the formation of a gel. Furthermore, the present invention provides an easy means of rapidly removing the gel tray and gel from the casting apparatus while minimizing the risk of damaging the gel.
The invention is an apparatus for casting an electrophoretic separation medium within a received gel tray having open ends. The apparatus is constructed from a U-shaped housing, made from a base-plate with upright proximal and distal walls. Shaft supports are permanently attached to the outer edge of the upper surface of the base-plate, between the proximal and distal walls. Shafts are mounted in holes drilled approximately halfway into the interior face of the proximal wall and the opposing faces of the shaft supports. The shafts pass through compression springs and holes in an upright partitioning sliding wall. The sliding wall is held parallel with the proximal and distal walls. The shafts provide a linear means of movement for the sliding wall and guidance for the compression springs. The compression springs apply constant pressure against the sliding wall such that the pressure is directed toward the distal wall. The region between the sliding and distal walls forms a casting chamber able to receive single or multiple gel trays. Gaskets lining the opposing or interior faces of the sliding and distal walls produce a liquid-tight seal at each end of a gel tray placed within the casting chamber. A groove cut into the upper surface of the sliding wall permits the user to retract the sliding wall toward the proximal wall with one hand. When the sliding wall is retracted, a gel tray may be rapidly and easily placed into or removed from the casting chamber.